Multiple position beam switching tube



Dec. 24, 1957 E. D. AYERS 2,817,785

MULTIPLE POSITION BEAM SWITCHING TUBE .Filed Jan. 26, 1954 2 She ets-Sheet 1 INVENTOR E. D. AYERS MULTIPLE POSITION BEAM SWITCHING TUBE Dec. 24, 195? 2 SheetsSheet 2 Filed Jan. 25, 1954 MULTIPLE POSITION BEAM SWITCHING TUBE Cit Earl D. Ayers, Cranbury, N. J., assignor to Burroughs This invention relates to magnetron type multiple position beam switching tubes and particularly to means for pre-setting or indexing the electron beam in such tubes to a pro-determined position.

Magnetron type multiple position beam switching tubes make use of crossed electrostatic and magnetic fields in their operation. Usually the magnetic field is provided by a hollow cylindrical permanent magnet which surrounds the tube and whose flux permeates the tube in lines which are substantially parallel to the elongated centrally disposed cathode electrode of the tube. A typical tube of this general type has at least two arrays of electrodes surrounding the elongated thermionic cathode. A hollow cylindrical array of symmetrically disposed beam forming and directing electrodes, surrounds the cathode and is concentric with respect to it.

Each spade electrode is insulated from the other spade electrodes and is usually connected to a source of potential which is positive with respect to the cathode through a spade impedance which is usually a resistor. The spade electrodes are usually coextensive in length with the electron emissive portion of the cathode and have a curved, usually U-shaped, transverse cross sectional configuration. The open part of the spade faces outwardly with respect to the cathode.

An array of symmetrically disposed electron receiving or target electrodes which has a larger diameter than the array of spade electrodes surrounds the spades and usually constitutes the outer array of electrodes of the tube. The target electrodes are equal in number to the spade electrodes, and each target is aligned with the space between two adjacent spades whereby electrons which pass through the space may impinge on the target electrode which is associated therewith. Like the spades, each target electrode is connected to a source of potential which is positive with respect to the cathode through an individual impedance member which is usually a resistor. The output signal from each target electrode is developed across its target impedance member.

Other types of multiple position beam switching tubes may have additional types of electrodes which serve special functions. For instance, in one such type, a slotted sleeve like hollow cylindrical anode electrode is disposed between the spades and the target electrode. The slots in the anode extend longitudinally thereof and are disposed in alignment with and opposite to the spaces between the various spades. This anode serves, among other things, as an electrostatic shield between the target and the spade electrodes in order that large voltage swings on the targets do not affect the beam switching and holding stability of the tube. In still another type of tube an array of rod-like switching electrodes is positioned between the targets and the spades, there being one of the rod-like switching electrodes disposed between an edge of each Z,8l'i,78fi Patented Dec. 24, 1957 2 All of the above mentioned tube types, and other similar types of tubes, operate substantially as follows: When all of the spades are at the potential of the spade power supply, the relationship between the electrostatic and magnetic fields within the tube and particularly in the cathodespade portion of the tube is such that electrons emitted from the cathode tend to follow curved paths around the cathode and substantially no electrons impinge on the spades or other outer electrodes of the tube. If, however, the potential on one of the spades is lowered to, or near to, the potential of the cathode, the configuration of the electrostatic field is changed, especially in the vicinity of the spade having the lowered potential, and a stream or beam of electrons is formed between the cathode and the leading edge of that spade. The edge of the spade to which the beam is attracted is determined by the direc tion of rotation of the electron beam within the tube which is determined by the polarity of the magnetic field which permeates the tube). The electron beam locks in at the edge of the spade which is furthest in the direction of the rotation of the electron beam, and this edge is commonly called the leading edge.

The electrons impinging on the edge of the spade cause electron flow through the spade impedance and if the spade .resistor valve is properly chosen, the electron flow through it reduces the potential of the spade sufliciently to maintain the beam locked in eventhough the external means for reducing the potential of the spade be removed.

In each of these tube types the beam is advanced from one beam position or spade to another by some means which causes the beam to fan out or widen so that parts of the beam impinge both on the spade upon which the beam is locked in and upon the spade which is adjacent thereto in thevdirection of rotation of the beam. When the electron impinges on the next adjacent spade a voltage drop the spade potential drops below a critical value, the electron beam, due to the influence of the magnetic field will advance to the next spade or beam position. The particular means utilized for causing the electron beam to fan or spread in order to switch from one beam position to another will be described in detail in connection with the specific embodiments of the present invention.

These tubes have found considerable use as counters, for example, and in other control or switching devices. At the end of each single operation, however, or, in response to controlled demands it is often desirable to pre-set or index the electron beam to a predetermined beam position. One way in which this may be done is to disconnect the cathode circuit, thus cutting off the beam and clearing the tube, and then manually grounding one of the spades in order to cause an electron beam to be re-formed between the cathode and the grounded spade. The disadvantages of resetting or indexing the beam in this manner is obvious when his considered that the beam may advance from one position to another at a rate of several megacycles per second. In comparison to this, the time required to manually reset and index the beam is very large. Other electronic means for accomplishing this result have been developed, but, in most cases, considerable current must be carried by the control device which cuts oti the electron beam in order to clear the tube, or the control pulses which are applied to the indexing spades must be of considerable magnitude.

Since pulses of large magnitude are not normally available as control pulses in computers or similar equipment, additional amplifier stages would be required in order to derive such control pulses. 'Such initial amplifier stages would add to the bulk of the equipment and would dissipate additional heat and thus further complicate the problem of cooling the equipment. Obviously also, any additional stages of amplification which were required in the control equipment would add to the cost of the equipment.

A principal object of the present invention is to provide an improved magnetron type multiple position beam switching tube.

Another object of the present invention is to provide an improved magnetron timebeam switching tube in which the beam may be indexed by means of controlled pulses which are available in the equipment with which the tube is to be used.

A further object of the present invention is to provide improved, fast acting means for indexing the electron beam of a magnetron type multiple position beam switching tube.

An additional object of the present invention is to provide an improved, more economical means of indexing the electron beam in a magnetron type multiple position beam switching tube.

In accordance with the present invention a magnetron type multiple position beam switching tube having a centrally disposed elongated cathode is surrounded by an array of spades and an outer array of target electrodes as mentioned previously. A grid may surround the centrally disposed cathode and an auxiliary cathode is disposed adjacent to the spade to which the electron beam is to be indexed. A grid may also be disposed between the auxiliary cathode and its spade and be biased to prevent electrons from the auxiliary cathode from impinging on the index spade while the tube is operated as a beam switching device. A negative pulse applied simultaneously to the grid which surrounds the centrally disposed cathode and to the auxiliary cathode cuts off momentarily electron flow to all spades, clearing the tube. In addition the negative pulse drives the auxiliary cathode negative with respect to its grid and causes electron fiow from the auxiliary cathode to the indexing spade and produces a potential drop across the spade impedance of the index spade. Thus, since the potential of the indexing spade is lowered, the electron beam from the centrally disposed cathode re-forms to the indexing spade.

Thus, the tube is indexed by the application of a pulse having an amplitude of only a few volts. Because the control pulse is applied only as a bias voltage, no power is needed to index the beam. Also, the indexing of the beam is rapidly and positively accomplished. More than one spade could have indexing means associated with it if needed to index the beam to different positions in response to different commands.

The invention as well as additional objects and advantages of the invention will be best understood from the following description when read in connection with the accompanying drawings, in which:

Fig. 1 is an isometric view, partly broken away, of a magnetron type multiple position beam switching tube constructed in accordance with the present invention;

Fig. 2 is a sectional view of the beam switching tube shown in Fig. 1;

Fig. 3 is a perspective View of the auxiliary grid-cathode assembly shown in Fig. 1;

Fig. 4 is a sectional view taken along the lines 33 of Fig. 3;

Fig. 5 is a perspective view of a self supporting grid structure which surrounds the centrally disposed principal cathode in a modification of the tube shown in Fig. 1;

Fig. 6 is a schematic view of the tube shown in Fig. 1 and a circuit for the operation thereof in accordance with the present invention;

Fig. 6a is a detailed view showing the relationship between the spade 16a and the grid-cathode assembly 24; and

Fig. 7 is a schematic view of a modified b switching tube and circuit for the operation of the same in accordance with the present invention.

Referring to Fig. 1, there is shown a magnetron type multiple position beam switching tube 10 having, within an hermetically sealed envelope 12, a centrally disposed electron emissive tubular thermionic cathode 14 which is surrounded by a plurality of concentric arrays of electrodes. The array of electrodes which is nearest to the cathode 14 comprises a plurality of beam forming and directing electrodes 16 which are usually called spade electrodes. Each of the spades are insulated from the others and are spaced substantially equi-distantly one" from another around the circumference of the array. The spades 16 are substantially equal in length to the electron emissive portion of the cathode 14 and have a curved, usually U-shaped, transverse cross sectional configuration.

The outer array of electrodes comprises a plurality of electron receiving target electrodes 18, the number of target electrodes 18 being equal in number to the number of spade electrodes 16. The target electrodes are usually coextensive in length with the spade electrodes. Each of the target electrodes 18 is disposed in alignment with the space between two adjacent spades 16 whereby electrons passing through the space may impinge on the target electrode 18.

The third array of electrodes comprises a plurality oi. rod-like beam switching electrodes or grids Zti, the number of switching grids 20 being equal to the number of spades 16 in the tubes. One of the switching grids 20 is disposed generally between the lagging edge 22 of each spade 16 and a target electrode 18.

Referring particularly to Figures 1, 3 and 4, a gridcathode assembly 24 comprising a hollow tubular grid 26 having a slotted or apertured portion 28 is disposed within the space partially enclosed by a spade 16a intermediate its ends. The slot or aperture 28 faces the spade 16a to allow the electrons emitted from cathode 30 to impinge on the spade 16a. The cathode 30, which is illustrated as being of the filamentary type, is disposed within the hollow grid 26 and is insulateditherefrom by the end bushings 32 which may be made of ceramic or other insulating material. The grid 26 has tabs 34 which extend through the top and bottom micas 36, 38 which maintain the electrodes in the desired spatial relationship one with another. The end bushings 32 may be eliminated if the filamentary cathode is threaded, for example, through appropriately centered apertures in the top and bottom micas 36, 38 to maintain the cathode 30 insulated from the grid 26.

Leads (not shown for the sake of clarity in the drawings) from the various electrodes in the tube 10 are brought out through the stem of the tube 10 to the base pins 40. The grid-cathode assembly or arrangement 24 may be utilized in any magnetron type beam switching tube having spade electrodes or electrodes serving a similar function. The tube 10 is surrounded by a hollow permanent magnet 42 which provides the magnetic field required for the operation of the tube.

Referring to Figs. 6 and 6a, the utility of the grid and auxiliary cathode is shown in connection with an electron beam indexing arrangement in accordance with the present invention and a conventional electron beam switching circuit.

Each of the spade electrodes 16 has an individual spade impedance or load resistor 44 through which the spade 16 is conductively connected to a source of positive potential 46, illustrated as a battery. Likewise, each of the targets 18 has an individual load impedance 48, illustrated as a resistor, through which the target is conductively connected to a source of positive potential 50, illustrated as a battery. There are ten beam positions in the tube 10, and these may be numbered 1-40 inclusive. The odd switching grids 20 are conductively connecltid through a common lead 52 through a resistor 54 to a positive bias source grids (those at the 2, 4, 6, etc. beam positions) are 56. The even switching conductively connected through a common lead 58 and a resistor 60 to a positive bias source 62. The beam switching potential, which is negative in polarity is applied to theappropriate one of the terminals 64, 66 and across the respective resistor 54, 60 to reduce the bias on the appropriate switching grid and cause the electron beam 68 of the beam switching tube It) to switch to the next beam position.

The operation of the tube 10 is as follows: The spadecathode potential is of such value that, in view of the magnetic field which permeates the tube particularly the spade-cathode area, electrons which are emitted from the cathode 14 travel in curved paths and substantially no electron flow to the outer electrodes takes place when .all the spades are at the same positive potential with respect to the cathode. However, if the potential of a spade 16 is lowered to, or near to, the potential of the cathode M, an electron beam 68 will be formed between the cathode 14 and the beam position at which the spade potential is lowered. The magnetic field tends to cause the electron beam 68 to rotate around the tube; the direction of rotation of the beam being determined by the polarity of the magnetic field. The electron beam 68 is advanced by applying a negative pulse to the appropriate switching grid 21 causing the beam to fan out and impinge on the next advanced spade. When the potential of the advanced spade is lowered sufficiently because of the potential drop across its spade resistor 4-4, due to the spade current, the electron beam 68 will transfer to and lock in on the leading edge of the advanced spade. An output signal, developed across the target impedance 48, may be taken from the output terminal 49 of each beam position.

The operation of the tube 10 thus far described, forms no part of the present invention. A beam switching tube having the switching grids and the operating characteristics hereinabove recited is described and claimed in the co-pending application of S. Kuchinsky and S. P. Fan, Serial No. 370,086, filed July 24, 1953, now Patent 2,721,955, entitled lvlulti-Position Beam Tube.

However, it is desirable to have means associated with the tube 10 which will cause the electron beam to be prcset or indexed at a predetermined beam position.

In accordance with the present invention an auxiliary grid-cathode assembly 24 is associated with the spade 16a to which the electron beam 68 is to be pre-set or indexed. The grid 26 is normally biassed sufficiently negative (as by the battery 74) with respect to the auxiliary cathode 36 to cut oil electron flow to the normally positive charged spade 16a. The auxiliary cathode 3t), illustrated as a filament, is heated by an external means, such as the battery 7%. Further, the auxiliary cathode is connected to ground through a resistor 72. The auxiliary cathode 30 may be charged negatively with respect to the grid 26 by the application to the input terminal 76 of a negative potential, such as a pulse, across the resistor 72.

The electron beam indexing arrangement shown in Fig. 6 includes both the grid-cathode assembly 13d previously described and the tube 78 in this instance illustrated as a triode and the resistor 80 which are in series with the principal cathode 1d of the beam switching tube It). The electron beam 68 is indexed to the spade 16a when a ne ative potential of sufiicient amplitude to cut off conduction through the tube 78 and to bias the auxiliary cathode 30 negative with respect to the grid 26 is applied to the input terminal 76.

Since the elccron beam 68 of the beam switching tube 18 may be locked in at any of the several beam positions of the tube, it is necessary to clear the tube by extinguishing the electron beam 68 prior to the indexing of the beam at the predetermined beam position. When the negative indexing pulse is applied to the terminal 76, the control grid 84 of the tube 78 is biassed negative and conduction through the tube '78 is cut-off, extinguishing the electron beam 68. The resistor which is connected between the cathode 82 and ground may in some cases be eliminated, but functions in the present case as a current limiting resistor.

When the negative pulse is applied to the input terminal 76 the auxiliary cathode 30 is driven below the biasing potential of the grid 26, and electrons are attracted from the auxiliary cathode 30 to the spade 16a which is at a higher potential. The electron flow to the spade Eda results in a potential drop across the impedance 44a of that spade, lowering the potential on the spade 16a to, or near to, the potential of the principal cathode 14. When this occurs, the electron beam 68 re-forms between the cathode 14 and the index position spade 16a. Although the electron beam is cut otf when the tube 10 is cleared and cannot re-form until the end of the negative pulse, the electron beam is re-formed to the index position since the RC time constant of the circuit of the spade 16a maintains this spade, at least momentarily, at a lowered potential after the end of the applied indexing pulse. The aforementioned RC time constant refers to the combination of spade resistor 451a. and the space capacity of the spade 1651.

Referring to Figs. 5 and 7, the tube 10a is identical to the tube 10 except that a grid surrounds the principal cathode 14. The grid 90 may be of the self-supporting type as shown or of any similar type. The grid 90 should be spaced close to the cathode to minimize any adverse effect it may tend to have on the sharpness of the beam.

The beam indexing function of the arrangement of Fig. 7 is similar to that of Fig. 6. In Fig. 7, however, the negative indexing pulse is applied to the grid 90 as well as to the auxiliary cathode 30. The electron beam 68 is cut oil by the field surrounding the grid 90, thus eliminating the need for the separate clearing tube 78 which was required in the indexing arrangement shown in Fig. 6.

Although the indexing arrangement in accordance with the present invention has been described in connection with negative indexing pulses or potentials, the grid '26 may be pulsed in a positive direction to cause conduction between the auxiliary cathode 30 and the spade 16a. Further, other means may be used for clearing the tube or for assuring that the beam will rotate within the tube until the electron beam locks in on the spade at which the grid-cathode assembly 24 is located. Further, tubes having grid-cathode assemblies 24 at a plurality of beam positions may be utilized to perform predetermined control functions. The grid-cathode assembly 24 may likewise take a variety of physical forms, the one shown being merely by way of example.

What is claimed is:

l. A magnetron type beam switching tube comprising means for generating an electron beam, a plurality of beam forming and directing electrodes disposed in spaced relationship to the electron beam generating means and with respect to each other and operable to switch the beam successively from one to another of the electrodes, an auxiliary cathode disposed adjacent to one of the beam forming and directing electrodes, and means responsive to the electron current travelling between the auxiliary cathode and the beam forming and directing electrode adjacent to which the auxiliary cathode is disposed for reducing the potential of the latter to thereby direct the beam thereto.

2. A magnetron type beam switching tube comprising a centrally disposed principal cathode capable of generating an electron beam, an array of spaced apart beam forming and directing electrodes disposed about said principal cathode, an auxiliary cathode disposed adjacent to one of the beam forming and directing electrodes, and means connected to the said one beam forming and directing electrode and responding to the electron current reaching the electrode from the auxiliary cathode for reducing the potential'of said electrode and thereby direct the beam thereto.

3. A magnetron type beam switching tube comprising a principal cathode capable of generating an electron beam, an array of spaced apart beam forming and directing electrodes, said array being disposed around said principal cathode, each of said beam forming and directing electrodes presenting a curved surface towards said principal cathode, an auxiliary cathode, said auxiliary cathode being disposed adjacent to one of said beam forming and directing electrodes and on the side thereof which is more remote from the principal cathode to allow an electron current to pass between the auxiliary cathode and said one electrode, and means connected to the latter electrode and responsive to the electron current provided by the auxiliary cathode for lowering the potential of the beam forming and directing electrode to thereby direct the beam thereto.

4. A magnetron type beam switching tube comprising, a principal thermionic cathode, a hollow tubular array of beam forming and directing electrodes, said array surrounding said principal cathode, each of said beam forming and directing electrodes having a generally U-shaped transverse cross-sectional configuration, the closed portion of the U-shaped formation of each of said electrodes facing the principal cathode, an auxiliary thermionic cathode extending into the space defined by the sides of one of the beam forming and directing electrodes, a control electrode disposed between said auxiliary thermionic cathode and the beam forming and directing electrode with which the auxiliary cathode is associated, the control electrode being capable of cutting off the electron flow between the auxiliary cathode and the associated beam forming and directing electrode, and means connected to the latter mentioned electrode and responsive to the c011- trolled electron flow between the auxiliary electrode and its associated electrode for lowering the potential of said electrode to index the beam thereto.

5. Beam switching and indexing.iapparatus comprising a magnetron type multiple position beam switching tube having a principal cathode capable of generating an electron beam, a plurality of arrays of individual electrodes including a spade array and a target array, an electrode of each of said arrays being associated together as a beam position, the number of beam positions being equal in number to the number of spade electrodes in said array, means for applying a potential to statically maintain each of the spade and each of the target electrodes at a positive potential with respect to the cathode, means for reducing the positive potential on selected ones of said spade electrodes in order to direct and advance the electron beam from beam position to beam position, an auxiliary cathode disposed adjacent to one of said spade electrodes and operable to provide flow of electrons thereto, an impedance connected to the latter mentioned spade electrode and effective to reduce the spade potential thereof upon receiving the electron flow from the auxiliary cathode, and means for momentarily extinguishing the electron beam of the principal cathode and for simultaneously biasing the auxiliary cathode to cause the flow of electrons therefrom to the adjacent spade electrode and thence to the impedance to thereby alter the potential of said electrode, the altered potential of said last mentioned electrode being momentarily maintained at said potential beyond the termination of the beam extinguishing means to cause the reformed beam to be directed only to said spade electrode.

6. Beam switching and indexing apparatus comprising a magnetron type multiple position beam switching tube having a cathode capable of generating an electron beam, a plurality of arrays of individual electrodes including a V spade array, a target array, and a switching grid array,

an electrode of each of said arrays being associated together as a beam position, the number of beam positions being equal in number to the number of spade electrodes in said array of spades, potential means for statically maintaining each of said spade electrodes and each of said target electrodes at a potential which is positive with respect to the cathode, a bias potential source, each of said switching grids being conductively connected thereto, means for selectively applying a further potential to predetermined ones of said switching grids to thereby advance the electron beam in said tube, an auxiliary cathode, said auxiliary cathode being disposed adjacent to one of said spade electrodes, a control electrode, said control electrode being disposed in the path of electrons emanating from said auxiliary cathode to thereby control the arrival of the electrons to the adjacent spade electrode, means for momentarily extinguishing the electron beam and for simultaneously biasing said control electrode to thereby pass electrons to the spade electrode associated therewith, and means connected to the spade electrode and for responding to the electron current to alter the potential thereon, the altered potential of the spade electrode being maintained beyond the termination of the beam extinguishing means to cause the newly formed beam to be directed only to said spade electrode.

References Cited in the file of this patent UNITED STATES PATENTS 

